In-situ photo-crosslinkable elastomer based on polyalphaolefin/halloysite nanohybrid

In this research, new injectable and in situ photocurable elastomeric nanohybrids have been fabricated from polyalphaolefin (PAO) resins and halloysite nanofiller. In this regard, the co-oligomerization of long α-olefin monomers (C6, C8 and C10) with alkenol counterparts was carried out via a simple cationic route to provide OH-functionalized PAOs. The newly formed PAO type copolymer resins as well as halloysite nanoclay were then equipped with photocurable CC bonds containing an acrylate moiety. After the characterization of the final chemical substances and also of the intermediate structures, experimentally and computationally by means of Density Functional Theory (DFT) calculations, the neat treated PAO and PAO/halloysite nanohybrids were subjected to a curing process by visible light irradiation (λ ∼ 475 nm, blue light). The crosslinking efficiency of the neat resins and the formed nanohybrid was evaluated using shrinkage strain-time curves and equilibrium swelling method. The suggested nanohybrid is not only biocompatible (96 % in the MTT assay), and hydrophilic (with a water contact angle of 61°), but also exhibits an easy, fast and robust curing process with great potential for coating and sealing technologies for medical devices.

Effect of bioactive glass-containing dentin adhesives on microshear bond strength of composite restorations

Background

In general, bioactive glasses (BAGs) can react with tissue minerals and promote remineralization. However, the application of BAG in bonding agents and its impact on bond strength remain uncertain due to insufficient information and limited research in this area.

Materials and Methods

This study employed a randomized controlled design to assess the effects of composite-bonding agents with varying BAG contents on shear bond strength and fracture pattern in sound and demineralized teeth, with and without thermocycling. Thus, 80 healthy third molars were randomly divided into two groups: sound teeth and demineralized teeth. Five bonding agents were applied to the prepared dentin surfaces, including four experimental composite-bonding agents with varying BAG content (0, 0.2, 0.5, and 2 wt%) and the Adper Single Bond commercial bonding as control. The shear bond strength of all samples was measured using a universal tester. The type of failure of each specimen was determined using a stereomicroscope. Kruskal-Wallis nonparametric test was performed on the obtained shear bond strength data followed by Mann-Whitney post hoc test with Bonferroni correction to determine statistical significance. The level of significance was considered P ≤ 0.05 for all tests and was adjusted by Bonferroni correction.

Results

Demineralization significantly decreased shear bond strength in the teeth samples. Adper Single Bond exhibited the highest shear bond strength values. The addition of BAG did not have a significant influence on shear bond strength, regardless of demineralization or thermocycling condition. Adhesive failure was the predominant type of failure in all groups.

Conclusion

The incorporation of BAG filler up to 2 wt% did not result in significant changes in shear bond strength. Experimental adhesive bonding agents with 2 wt% BAG content demonstrated shear bond strengths comparable to the commercial bonding agent in sound nontreated, sound thermocycled, demineralized nontreated, and demineralized thermocycled groups.

Solution photo-copolymerization of acrylic acid and itaconic acid: The effect of polymerization parameters on mechanical properties of glass ionomer cements

OBJECTIVE

To synthesize a series of poly (acrylic acid-co-itaconic acid) (P(AA-co-IA)) copolymers with different molecular weights (MWs) through a facile water-based solution photopolymerization and to investigate the operational and mechanical properties of the experimental glass-ionomer (GI) cements made of the ionomers.

METHODS

Thioglycolic acid (TGA) was used as a chain transfer agent to synthesize P(AA-co-IA) ionomers with different MWs through the solution photopolymerization. The chemical structure, MWs, and rheological properties of the copolymers were fully characterized. The GI cements were prepared using the ionomer solutions in different MWs and concentrations. Finally, the operating and mechanical properties of the experimental GI cements were investigated and compared with those of a commercially available GI cement.

RESULTS

The synthesis and composition of the P(AA-co-IA) were approved by spectroscopy analyses. The results revealed that by increasing the TGA content, MW and polydispersity index (PDI) of the synthesized copolymers demonstrate a decreasing trend from 4.5 × 104 g/mol (PDI of 2.45) to 7.4 × 103 g/mol (PDI of 1.62). Accordingly, the viscosity of copolymers decreased with increasing the TGA concentration in the polymerization recipes. Setting times of the cements increased with reducing the MWs and ionomer concentration. The compressive and flexural strengths of GI cements were improved by increasing the MWs, ionomers concentration, and storage time.

SIGNIFICANCE

The solution photopolymerization provides a facile and environmentally safe method to synthesize P(AA-co-IA) copolymers with controlled MWs. The structure-property relationships presented in the study also provide valuable information in the production and improvement of the GI cements.

Effect of zinc oxide nanoparticles on physical and antimicrobial properties of resin-modified glass ionomer cement

Background:

To improve the limitations, many modifications in the resin-modified glass ionomer (RMGI) composition have been proposed. In this study, we evaluated the effect of different concentrations of zinc oxide (ZnO) nanoparticles incorporated into RMGI cement on its physical and antimicrobial properties.

Materials and Methods:

In this in vitro study, ZnO nanoparticles with 0–4 wt.% concentrations were incorporated into RMGI. The following tests were carried out: (a) Antibacterial activity against Streptococcus mutans tested by disc diffusion method, (b) mechanical behavior assessment by measuring flexural strength (FS) and flexural modulus (FM), (c) micro-shear bond strength (μ-SBS), and (d) fluoride and zinc release. Data were analyzed using the statistical tests of ANOVA, t-test, and Tukey's HSD post hoc in SPSS V22. The level of significancy was 0.05.

Results:

In the disc diffusion method, specimens with 2 wt.% ZnO nanoparticles showed the highest antimicrobial efficacy (P < 0.05). After 1 month of water storage, no significant difference was observed in FS and FM of the samples (P > 0.05). In 2 wt.% ZnO nanoparticles group, μSBS increased in the first 7 days but decreased by 17% after one month, which showed a significant difference with that of the control group. The fluoride release did no change in the ZnO nanoparticle-containing group compared with the control group at all time intervals.

Conclusion:

Incorporation of 2 wt.% ZnO nanoparticles into the RMGI cement adds antimicrobial activity to the cement without sacrificing FS and fluoride release properties, while decreased μSBS.

Poly(hydroxybutyrate-co-hydroxyvalerate) Porous Matrices from Thermally Induced Phase Separation

Thermally induced phase separation followed by freeze drying has been used to prepare biodegradable and biocompatible scaffolds with interconnected 3D microporous structures from poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) copolymers containing 5 and 12 wt % of 3-hydroxyvalerate (HV). Solutions of PHBV in 1,4-dioxane, underwent phase separation by cooling under two different thermal gradients (at -25 °C and -5 °C). The cloud point and crystallization temperature of the polymer solutions were determined by turbidimetry and differential scanning calorimetry, respectively. Parameters affecting the phase separation mechanism such as variation of both the cooling process and the composition of the PHBV copolymer were investigated. Afterwards, the influence of these variables on the morphology of the porous structure and the final mechanical properties (i.e., rigidity and damping) was evaluated via scanning electron microscopy and dynamic mechanical thermal analysis, respectively. While the morphology of the scaffolds was considerably affected by polymer crystallization upon a slow cooling rate, the effect of solvent crystallization was more evident at either high hydroxyvalerate content (i.e., 12 wt % of HV) or high cooling rate. The decrease in the HV content gave rise to scaffolds with greater stiffness because of their higher degree of crystallinity, being also noticeable the greater consistency of the structure attained when the cooling rate was higher. Scaffolds were fully biocompatible supports for cell adhesion and proliferation in 3D cultures and show potential application as a tool for tissue regeneration.

Synthesis and characterization of core-shell nanoparticles and their application in dental resins

The aim of this study was to synthesize acrylic core-shell particles and silica-loaded core-shell hybrid particles through emulsion polymerization. Also this work examined the influence of synthesized nanoparticles loading in a Bis-GMA/TEGDMA resin matrix on some mechanical properties of the dental composite resins. Core-shell particles consisting of polybutyl acrylate (PBA) rubbery core and polymethyl methacrylate (PMMA)/polystyrene (PS) shell were synthesized by seeded emulsion polymerization. For preparing the core-shell hybrid particles, first silica particles with diameters of about 68 nm were synthesized based on the Stöber process. Then the surface of silica particles was treated with ɣ-MPS. Afterwards, polymeric shell was coated on silica nanoparticles through emulsion polymerization. The morphology of core-shell particles was examined by SEM/TEM. Mechanical properties (fracture toughness, flexural strength and flexural modulus) of the photo-cured Bis-GMA/TEGDMA dental resins/composites filled with different mass fractions of synthesized nanoparticles were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. Formation of glassy shell on PBA core in core-shell particles, grafting of ɣ -MPS onto the silica particles and encapsulation of modified silica by polymeric shell in core-shell hybrid particles were confirmed using various analytical techniques. The results of mechanical tests showed that fracture toughness of Bis-GMA/TEGDMA dental resins improved about 35% by the inclusion of 5 wt% silica-loaded core-shell hybrid particles with little effect on flexural strength. This study shows that incorporation of proper amount of hybrid core-shell particles in dental composites can improve their fracture toughness and thus may extend their service life.

Dual modified nanosilica particles as reinforcing fillers for dental adhesives: Synthesis, characterization, and properties

A facile procedure has been devised to develop a novel dentin bonding system containing poly (acrylic acid)-grafted-silanized fumed silica particles as reinforcing filler, with high stability of nanoparticle dispersion and enhanced bond strength and mechanical properties. In the first step, the silanization of fumed silica nanoparticles was performed in the following conditions: (i) ethanol-water solution with a pH of 5 and (ii) cyclohexane with a pH of 9 using trimethoxysilylpropyl methacrylate (γ-MPS) as a reactive silane coupling agent. FTIR and TGA analyses confirmed the presence of silane in the resultant structure and enhanced dispersion stability of modified particles was proved by a separation analyzer and also zeta potential analyses. In the second step, free radical polymerization of acrylic acid monomers in the presence of silanized nanoparticles was carried out and poly (acrylic acid) -grafted- silanized fumed silica were acquired. The flexural strength and fracture toughness of the adhesive containing 0.2 wt.% of the dual modified filler reached maximum of 70.4 MPa and 1.34 MPa m^1/2, respectively, showing average improvements of 74% and 179%, respectively, in comparison with the adhesive without filler. Flexural modulus values did not significantly change with increasing the filler content except the adhesive containing 5 wt.% having the lowest flexural modulus. The highest microtensile bond strength was also observed at 0.2 wt.% filler content showing the average improvements of 197% as compared with the neat adhesive. Energy dispersive X-ray (EDX) mapping confirmed a homogenous and uniform distribution of the fillers in the adhesive matrix containing 0.2 wt.% and 0.5 wt.% of filler while incorporation of 5 wt.% led to large particle aggregates. SEM images of the fracture surface of the adhesive with different filler contents subjected to fracture toughness test showed rougher surface and longer crack path by increasing filler concentration. The adhesive containing 0.2 wt.% of filler perfectly penetrated into the dentin tubules proved by the SEM micrographs in microtensile bond strength test.

Poly (methacrylic acid) modified spherical and platelet hybrid nanoparticles as reinforcing fillers for dentin bonding systems: Synthesis and properties

OBJECTIVE

In this study the mechanical and adhesion properties of an experimental methacrylate based dentin bonding system containing a combination of spherical and layered platelet nanoparticles were investigated. The nanoparticles were first modified through surface graft polymerization of methacrylic acid in order to make the particles surface compatible with the bonding matrix resin.

MATERIALS AND METHODS

Graft free radical polymerization in aqueous media was performed to attach Poly (methacrylic acid) (PMA) chains onto the surface of Na-MMT nanoclay (Cloisite® Na+) and silica nanoparticles (Aerosil® 200). The hybrid PMA grafted nanoparticles (PMA-g-NC-Sil) were characterized using GPC, FTIR, TGA, and X-ray diffraction (XRD). Dentin adhesives containing different amounts of the hybrid modified nanoparticles were photopolymerized and their characteristics were studied using FTIR, TEM, SEM, EDXA, and XRD techniques. The adhesives containing different amounts of PMA-g-NC-Sil were applied to the conditioned human premolar dentin to bond a dental composite to the teeth. The bond strength was then measured by microshear bond strength testing method. The results were analyzed and compared statistically. The stability of PMA-g-NC-Sil dispersion in the dentin adhesive was investigated using separation analysis (LUMi Reader) techniques.

RESULTS

The grafting of PMA chains onto the surface of nanoclay was confirmed by FTIR and TGA analytical techniques. The intercalated-exfoliated structure for the nanoclay platelets in the photo-cured adhesive was observed using XRD and TEM. The surface modification of the nanoparticles significantly increased the dispersion stability of the fillers in the adhesive solution. The microshear test results indicated that the incorporation of the PMA-g-NC-Sil nanoparticles significantly enhanced the bond strength to dentin with the highest shear bond strength observed at 0.5 wt%.

SIGNIFICANCE

The incorporation of the PMA modified hybrid nanofillers into the dentin adhesive resulted in a dentin bonding agent with enhanced shear bond strength through reinforcing the adhesive matrix and potential interactions between their carboxylic acid groups and the tooth structure. The dispersion stability of the nanoparticles was also dramatically improved by the surface modification of the nanoparticles.

Synthesis of poly(acrylic-co-itaconic acid) through precipitation photopolymerization for glass-ionomer cements: Characterization and properties of the cements

OBJECTIVE

The aim of this study was to synthesize poly(acrylic acid-co-itaconic acid) (PAA-co-PIA) ionomer through a novel precipitation photopolymerization technique. The ionomer was characterized and the effect of its structural parameters, such as molecular weight and copolymer composition were investigated on the mechanical properties of glass-ionomer prepared using the ionomer.

METHODS

Design of experiment (DOE) was used to examine the effect of monomer ratio and the amount of chain transfer agent on the molecular weight and final conversion of the ionomers synthesized through the precipitation photopolymerization. The copolymer compositions were identified using FTIR and ¹H-NMR spectroscopy. The molecular weights of the copolymers were evaluated by GPC. A series of PAA-co-PIA copolymers were then synthesized via the photopolymerization technique in three monomer ratios and two molecular weight ranges (high and low) to study the properties of the glass ionomers thereof. Experimental dental glass-ionomer cements were prepared by mixing the synthesized polymers with glass powder and their compressive properties were determined according to ISO 9917-1:2007 after storing for 0, 1, 7 and 28 days in distilled water. The scanning electron microscopy (SEM) was used to study the fracture surface morphology of the cements.

RESULTS

The PAA-co-PIA polymers were synthesized by the photopolymerization method in a short time and high purity. The DOE showed that by decreasing the acrylic acid/itaconic acid ratio and increasing the amount of transfer agent, the molecular weight and final conversion decreased significantly. By increasing the itaconic acid content in the copolymer composition and increasing the molecular weight in a constant copolymer composition, the compressive strength and modulus were increased. Microstructures revealed that cements made of the higher molecular weight poly acids showed lower cracks and voids.

SIGNIFICANCE

The precipitation photopolymerization technique provides a promising and facile method in the synthesis of ionomers which are used in dental cements and other application.

A novel thymol-doped enamel bonding system: Physico-mechanical properties, bonding strength, and biological activity

PURPOSE

Over the past decades, the preparation of antibacterial restorative dental adhesives has obtained increasing attention in order to prevent secondary caries. In the present study, a novel essential oil-based antibacterial resin adhesive was prepared and evaluated for dental applications. In this regards, thymol, which is a major phenolic component of thyme essential oil, was incorporated into methacrylate resin matrix and its effect on the physico-mechanical and biological properties of the experimental bonding agent was investigated.

MATERIALS AND METHODS

Mechanical properties were evaluated via measuring flexural strength, flexural modulus and fracture toughness. Degree of conversion (DC%) of monomers was measured using FTIR spectroscopy. Viscoelastic properties of the samples were also determined by dynamic mechanical thermal analysis (DMTA). The bactericidal activity of composite specimens against Streptococcus mutans (ATCC 35668) was determined based on ASTM E 2180-07.MTT assay was performed to investigate the cytocompatibility of samples. Furthermore, the bonding strength of the adhesives was evaluated through microshear bond test on the caries-free extracted human premolar teeth and the mode of failure was investigated by scanning electron microscopy.

RESULTS

Thymol-doped resin adhesive exhibited comparable degree of conversion to the control resin adhesive. The plasticizing behavior of thymol slightly decreased the flexural modulus and glass transition temperature of the thymol containing specimens, even though; it caused significant increases in fracture toughness of adhesive. The results represented appropriate antibacterial activity as well as suitable cytocompatibility. Furthermore, the thymol-doped resin adhesive showed comparable adhesive strength to the control.

CONCLUSION

The thymol is extremely compatible with the methacrylate resin restorative system and completely fulfills all requirements of a good bactericidal component in construction of an ideal enamel bonding system.

The Effect of Incorporation of 0.5 %wt. Silica Nanoparticles on the Micro Shear Bond Strength of a Resin Modified Glass Ionomer Cement

STATEMENT OF THE PROBLEM

The clinical success of glass ionomer restorations depends on the strength of resin-modified glass ionomer (RMGI) cement bonding to dentin and there is limited information available regarding the bond strength of resin modified glass ionomers containing silica nanoparticles to dental structures.

PURPOSE

The aim of this study was to compare the microshear bond strength (µSBS) of RMGI with and without silica (SiO2) nanoparticles to dentin of permanent teeth.

MATERIALS AND METHOD

In this experimental study, the occlusal surfaces of 30 freshly extracted intact third molars were ground to expose the flat dentin and after conditioning with 20% poly acrylic acid, were randomly assigned to two main groups (n=15). The first group was filled with RMGI (Fuji II LC, GC) and the second group was filled with RMGI plus 0.5%wt. silica nanoparticles. Then, each main group was divided into three subgroups, and then stored in an incubator at 37 oC with 100% humidity for 1, 7, and 30 days. The µSBS test was performed using a universal testing machine (1 mm/min). The data were analyzed by t-test, repeated measures ANOVA and Tukey test (p< 0.05).

RESULTS

There were no statistically significant differences between the mean µSBS of the groups with and without nanoparticles along the different storage periods (p> 0.05). There was significant difference in µSBS values among the three different storage periods in all the tested materials (p< 0.05).

CONCLUSION

Incorporation of 0.5 %wt. silica nanoparticles did not compromise the µSBS of Fuji II LC RMGI to dentin.

Effect of rinsing time and surface contamination on the bond strength of silorane-based and dimethacrylate-based composites to enamel

Background

The aim of this study was to assess whether saliva contamination and rinsing time for 15, 30, and 60 seconds, affects the shear bond strength of silorane and methacrylate-based composites to enamel.

Material and Methods

Two light cure resin, P60 (3M ESPE) and Filtek LS Silorane were tested. 120 sound premolars were randomly divided into four groups of 30 teeth based on composite type with or without saliva contamination after etching and rinsing. Each group was further divided into three subgroups according to their rinsing time. Then a cylinder of the composite was bonded to the enamel and Shear bond strength was assessed. To determine the failure mode, the bonded surfaces were then observed under SEM. In addition, the DC of each group was measured at pH levels of 4 and 7 using FTIR spectroscopy. The data were analyzed with one-way ANOVA and post hoc analysis followed by Fisher’s least significant difference.

Results

The bond strength of the non-contaminated methacrylate group was significantly higher than the other groups (p< 0.0001). In addition, there was no significant deference between the methacrylate subgroups. In the silorane groups, the shear bond strength was higher in the rinsing time of 15 seconds. Failure pattern was mainly adhesive. The DC of the Methacrylates had no significant difference at pH 4 and pH 7, but was significantly higher than that of siloranes (p< 0.0001). While the DC of the siloranes at pH 4 was significantly higher than at pH 7 (p< 0.0001).

Conclusions

Saliva contamination in both composites reduces bond strength. Increasing rinsing time in Methacrylates proves ineffective. In non-contaminated siloranes, excessive rinsing time reduced bond strength. The best-recommended rinsing time for both composite is 15 seconds.

Key words:Composite resins, silorane composite resin, methacrylates, shear strength.

In vivo study of antifungal effects of low-molecular-weight chitosan against Candida albicans

This study investigated the antifungal effects of low-molecular-weight chitosan solution on Candida albicans in denture stomatitis in comparison with nystatin suspension. This randomized, sing-leblind clinical trial included 40 patients diagnosed with denture stomatitis. Patients were divided into two groups, wherein one was treated with chitosan and the other with nystatin for 2 weeks. Changes in the erythematous area were recorded during and after treatment. A palatal smear was obtained for each patient before and after treatment to determine the number of blastospores and mycelia of C. albicans. The results were compared using the Mann-Whitney U test, revealing that the chitosan solution significantly decreased the erythematous surface area, burning sensation, time required for clinical improvement, and number of blastospores and mycelia. The antifungal efficacy of chitosan along with its inherent biocompatibility makes it a promising candidate for use as an antifungal mouthwash.

Effects of ethanol concentrations of acrylate-based dental adhesives on microtensile composite-dentin bond strength and hybrid layer structure of a 10 wt% polyhedral oligomeric silsesquioxane (POSS)-incorporated bonding agent

Background

The aim of this study was to assess for the first time the effects of different amounts of ethanol solvent on the microtensile bond strength of composite bonded to dentin using a polyhedral oligomeric silsesquioxane (POSS)-incorporated adhesive.

Materials and Methods

This experimental study was performed on 120 specimens divided into six groups (in accordance with the ISO TR11405 standard requiring at least 15 specimens per group). Occlusal dentin of thirty human molar teeth was exposed by removing its enamel. Five teeth were assigned to each of six groups and were converted to 20 microtensile rods (with square cross-sections of 1 mm × 1 mm) per group. The "Prime and Bond NT" (as a common commercial adhesive) was used as the control group. Experimental acrylate-based bonding agents containing 10 wt% POSS were produced with five concentrations of ethanol as solvent (0, 20, 31, 39, and 46 wt%). After application of adhesives on dentin surface, composite cylinders (height = 6 mm) were bonded to dentin surface. The microtensile bond strength of composite to dentin was measured. The fractured surfaces of specimens were evaluated under a scanning electron microscope to assess the morphology of hybrid layer. Data were analyzed using one-sample t-test, one-way analysis of variance (ANOVA), and Tukey tests (α = 0.05).

Results

the mean bond strength in the groups: "control, ethanol-free, and 20%, 31%, 39%, and 46% ethanol" was, respectively, 46.5 ± 5.6, 29.4 ± 5.7, 33.6 ± 4.1, 59.0 ± 5.5, 41.9 ± 6.2, and 18.7 ± 4.6 MPa. Overall difference was significant (ANOVA, P < 0.0001). Pairwise differences were all significant (Tukey P < 0.05) except those of "ethanol 0% versus 20%" and "20% versus 31%." All groups except "0% and 46% ethanol" had bond strengths above 30 MPa (t-test P < 0.05).

Conclusion

Incorporation of 31% ethanol as solvent into a 10 wt% POSS-incorporated experimental dental adhesive might increase the bond strength of composite to dentin and improve the quality and morphology of the hybrid layer. However, higher concentrations of the solvent might not improve the bond strength or quality of the hybrid layer.

Correction to: Cure kinetic study of methacrylate-POSS copolymers for ocular Lens

The original version of this article unfortunately contained a mistake: the spelling of the Ebrahim Gafar-Zadehs' name was incorrect. The corrected name is given above.

Correction to: Compositional design and Taguchi optimization of hardness properties in silicone-based ocular lenses

The original version of this article unfortunately contained a mistake: The spelling of the Ebrahim Gafar-Zadehs' name was incorrect. The corrected name is given above.

Casein phosphopeptide- amorphous calcium phosphate effects on brackets shear bond strength and enamel damage

Background

The aim of study was to evaluate the application of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and fluoride regarding their effect on the shear bond strength (SBS), bond failure pattern of brackets using the adhesive remnant index (ARI) and assessing the quality of enamel surface using the enamel damage index (EDI).

Material and Methods

Sixty extracted premolar teeth were randomly divided into four groups regarding pretreatment application of CPP-ACP and fluoride. Brackets were bonded using the conventional method. Specimens were thermocycled for 1000 cycles and were subsequently tested for the SBS in a universal testing machine. After debonding, the teeth were examined under a stereomicroscope to evaluate the ARI. Then, The EDI was assessed using a scanning electron microscope (SEM). Data were analyzed using ANOVA and the Chi-square test.

Results

Evaluation of SBS, ARI and EDI scores showed no significant difference among the study groups. However, a correlation was found between the ARI and EDI scores, indicating that with more adhesive remnants on enamel surface, enamel damage was lower.

Conclusions

The use of CPP-ACP and fluoride can be considered a prophylactic application since these agents did not compromise bracket bond strength although they did not reduce iatrogenic damage to the enamel.

Key words:CPP-ACP, Enamel damage, SEM, Shear bond strength, ARI.

Dentin bonding agent with improved bond strength to dentin through incorporation of sepiolite nanoparticles

Background

The study aims to investigate the effect of incorporation of sepiolite nanoparticles on the microtensile bond strength of an experimental dentin bonding to the human dentin.

Material and Methods

The sepiolite nanoparticles were incorporated into an experimental methacrylate-based dentin bonding system in concentrations of 0.0, 0.2, 1.0, 2.0, and 5.0 weight percents. The specimens were then ultrasonicated to finely disperse the nanoparticles in the adhesive matrix. The coronal enamel of 30 intact human premolars was cut to expose dentin. Having etched, rinsed, and blot dried the experimental bonding agents were applied to dentin surface. Adper Single Bond was used as control group according to the manufactor’s instruction. Then all the teeth were built up by composite and sectioned in stick form for microtensile test. The fracture surface was observed using SEM. The data were analyzed by ANOVA and Tukey’s post-Hoc test.

Results

The results indicated that the incorporation of the nanofiller, improved the bond strength to dentin with the highest values obtained at 1 w% sepiolite nanoparticle content.

Conclusions

Sepiolite nanoparticles can be considered as novel fillers to improve the mechanical properties of dentin bonding agents.

Key words:Dentin bonding agent, nanoparticles, bond strength, sepiolite, microtensile test.

Fabrication of denture base materials with antimicrobial properties

STATEMENT OF PROBLEM

Acrylic resin denture base resins are colonized by oral and nonoral bacteria and Candida species. This reservoir of microorganism causes denture stomatitis, which can be implicated in some life-threating infections in older denture wearers.

PURPOSE

The purpose of this in vitro study was to incorporate quaternized N,N-dimethylaminoethyl methacrylate (DMAEMA) monomer into a denture base resin and investigate its antimicrobial and mechanical properties.

MATERIAL AND METHODS

Quaternized ammonium monomer (QAM) was synthesized through the reaction of octyl bromide and DMAEMA. The synthesized QAM was incorporated into a denture base resin system (8 to 12 wt%). The resulting material was characterized by Fourier transform infrared spectroscopy. The in vitro antimicrobial property was determined by direct contact test against Escherichia coli, Staphylococcus aureus, and Candida albicans. Release of the QAM was also tested by means of an agar diffusion test. Mechanical properties were measured with a 3-point bend test, and results were analyzed and compared using ANOVA and the Tukey post hoc test (α=.05).

RESULTS

Spectroscopy confirmed the formation of quaternized ammonium modified denture base (QAMDB). The decrease in number of viable cells of E coli, S aureus, and C albicans was more than 99% for 12%-QAMDB in comparison with that of the control groups. An overall decline was observed in the flexural strength and flexural modulus of the fabricated resins (P<.05), but no differences were observed for strain at break or fracture work of the specimens (P>.05).

CONCLUSIONS

Denture base resins containing immobilized QAM provided high antibacterial activity, but the flexural strength and flexural modulus of the denture base resins decreased.

Effect of addition of Nano hydroxyapatite particles on wear of resin modified glass ionomer by tooth brushing simulation

Background

Recently, incorporation of nanohydroxyapatite (NHA) has been suggested to improve the mechanical properties of glass ionomers (GIs). This study aimed to assess the effect of addition of NHA on wear of resin modified glass ionomer (RMGI) by tooth brushing simulation.

Material and Methods

In this in vitro, experimental study, NHA in 1, 2, 5, 7 and 10wt% concentrations was added to Fuji II LC RMGI powder, and 48 samples (5×5mm) in five experimental and one control group (n=8) were fabricated. After polishing, cleaning and incubation at 37°C for three weeks, the samples were weighed and subjected to tooth brushing simulation in a toothpaste slurry according to ISO14569-1. Then, they were weighed again and the weight loss was calculated. The data were analyzed using one-way ANOVA and Tukey’s test.

Results

The highest and the lowest weight loss was found in the 0% NHA (-1.052±0.176) and 5% NHA (-0.370±0.143) groups, respectively. Wear was significantly higher in 0% NHA group (P<0.05). No difference was detected in wear between 2 and 5wt% NHA or among 1, 7 and 10wt% NHA groups. Significant differences were noted in wear between 2 and 5wt% NHA and 1, 7 and 10wt% NHA groups (P<0.001).

Conclusions

Incorporation of up to 10wt% of NHA increases the wear resistance of Fuji II LC RMGI. This increase was the highest when 2 and 5wt% NHA were added.

Key words:Glass ionomer, hydroxyapatites, nanoparticles, dental restoration wear.

The effect of acrylate-based dental adhesive solvent content on microleakage in composite restorations

Background:

This study aimed to evaluate the effect of different percentages of ethanol solvent of an experimental methacrylate-based dentin bonding agent containing polyhedral oligomeric silsesquioxanes (POSS) on the microleakage of resin composite restorations.

Materials and Methods:

In this experimental study, 42 extracted human premolar teeth used and 84 standard Class V cavities were prepared on the buccal and lingual surfaces of the teeth. The teeth were divided into 6 groups of 7. Experimental bonding agents with different percentages of solvent were used in 5 groups and Single Bond^® as a control. The teeth were restored with resin composite and subjected to thermal cycling test. Teeth were then immersed in a solution of 2% basic fuchsine dye for 24 h and sectioned buccolingually and scored using stereomicroscope with ×32 magnification. Microleakage data were analyzed using the Kruskal–Wallis, Mann–Whitney U, and Wilcoxon tests.

Results:

There were significant differences between the microleakage enamel margins (P = 0.036) and dentinal margins (P = 0.008) in all the groups. These significant differences were seen between the control group and groups containing 46 wt% solvent (P = 0.011), 46 wt% and 31 wt% solvent in dentinal (P = 0.027), 31 wt% and 0 wt% in enamel (P = 0.021), also 0 wt% and control in enamel (P = 0.039), and dentinal margins microleakage (P = 0.004). The microleakage in dentinal margins was higher than enamel margins (P < 0.001). In the groups with 46 wt% solvent (P = 0.103), 0 wt% (P = 0.122), and control group (P = 0.096), however, this difference was not significant.

Conclusion:

The adhesive containing 31 wt% solvent showed the least marginal microleakage, presence of POSS filler may also result in the reduction of microleakage.

Bactericidal dental nanocomposites containing 1,2,3-triazolium-functionalized POSS additive prepared through thiol-ene click polymerization

OBJECTIVE

Deterioration of mechanical strength for the dental composite containing ionic bactericidal compounds restricts the widespread utilization of this class of useful materials. This problem is originated from the reduction of the intermolecular interaction of polymeric network due to plasticization effect of absorbed water molecules penetrated between the chain segments. The main goal of this study is the synthesis of the highly efficient bactericidal additive with low hydrophilicity and consequently the least adverse effect on the final mechanical strength of the dental composite.

METHODS

The bactericidal 1, 2, 3-triazolium functional groups were chemically anchored on the surface of hydrophobic POSS nanoparticles (Triazolium-POSS) and incorporated into a dental restorative system composed of a ternary thiol-allyl ether-methacrylate resin and glass fillers. A similar system was also prepared, in which the POSS additive was replaced with quaternized dimethyl aminoethyl methacrylate monomer (DMAEMA-BC). The chemical structure of POSS derivatives was evaluated by ¹HNMR and FTIR spectra. The water uptake of dental composites was evaluated at days 1 and 14 after immersion into water. The bactericidal activity of composite specimens against Streptococcus mutans (ATCC 35668) was determined based on ASTM E 2180 - 07. The flexural properties of samples were investigated through three-point bending assay and the shrinkage-strain of photo-cured resins was measured using the bonded-disk technique. The degree of conversion (DC %) of methacrylate functions was followed by FTIR spectroscopy. MTT assay was performed to investigate the cytocompatibility of samples.

RESULTS

Regardless of the partial increase in water uptake for Triazolium-POSS-containing sample, this parameter was much favor than the composite made from DMAEMA-BC. Therefore, the lower decline in flexural properties was recorded under the wet condition for the former system. Incorporation of Triazolium-POSS had no significant effect on shrinkage strain and cytocompatibility of composite specimen, meanwhile, a higher degree of conversion of methacrylate functional groups was recorded. The Triazolium-POSS-containing nano composite showed significantly higher bactericidal activity against Streptococcus mutans than another studied model system.

SIGNIFICANCE

The new derivative of bactericidal POSS nanoparticles decorated with 1, 2, 3-Triazolium moieties is a highly efficient bactericidal compound. If Triazolium-POSS is incorporated into a proper dental resin formulation, it can provide a strong bactericidal activity for dental materials; in the meantime, it leads to minimum deterioration of their mechanical strength due to its low water uptake.

In-situ photocrosslinkable nanohybrid elastomer based on polybutadiene/polyhedral oligomeric silsesquioxane

Hydroxyl functionalized nano-sized POSS or ethyleneglycol as diol monomers was incorporated to hydroxyl-terminated polybutadiene (HTPBD) chain in the presence of fumaryl chloride as extender. Blue light photocrosslinking system based on camphorquinone (photoinitiator) and dimethylaminoethyl methacrylate (accelerator) was applied to cure these two synthesized fumarate based macromers. Self-crosslinkability of unsaturated macromers and also crosslinking in presence of a reactive diluent were investigated in absence and presence of 1,4-butanediol dimethacrylate, respectively. Finally, photocured samples were characterized by XRD, SEM, equilibrium swelling study, TGA, DMTA, AFM and cell culture. The results showed that incorporation of POSS nanoparticle into the polymer matrix with a perfect distribution and dispersion can enhance thermal stability, mechanical and biocompatibility properties which can prove a good potential of this in-situ photocrosslinkable nanohybrid in medical applications.

The effect of silica nanoparticles on the mechanical properties of fiber-reinforced composite resins

Background. Nanotechnology has introduced many nanoparticles in recent years, which can be incorporated for mechanical improvement of dental materials. However, the existing data are widely sparse. This study investigated the reinforcing effect of silica nanoparticles when incorporated into the matrix phase of an experimental dental fiber-reinforced compositeresin (FRC) through evaluation of its flexural properties.

Methods. In this experimental study FRC samples were divided into two main groups (containing two or three bundles),either of whic consisted of five subgroups with 0, 0.2, 0.5, 2 and 5 wt% of silica nanoparticles in the matrix resin (n=10 in each subgroup); a commercial FRC (Angelus, Brazil) was used as the control group (n=10). Three-point bending test was performed to evaluate the flexural strength and modulus. Thereafter, the microstructure of the fractured samples was evalu-ated using scanning electron microscopy (SEM). The results were analyzed with one-way ANOVA and HSD Tukey tests (α = 0.05).

Results. The results revealed that the silica nanoparticles had a significant and positive effect on the flexural strength and modulus of FRCs (P<0.05), with no significant differences from 0.2 to 5 wt% of nanoparticles (P > 0.05) in either group with two or three bundles of fibers.

Conclusion. Incorporating silica nanoparticles into the FRC resin phase resulted in improved flexural strength and modulus of the final product.

Effect of fiber diameter on flexural properties of fiber-reinforced composites

BACKGROUND

Flexural strength (FS) is one of the most important properties of restorative dental materials which could be improved in fiber-reinforced composites (FRCs) by several methods including the incorporation of stronger reinforcing fibers.

AIM

This study evaluates the influence of the glass fiber diameter on the FS and elastic modulus of FRCs at the same weight percentage.

MATERIALS AND METHODS

A mixture of 2,2-bis-[4-(methacryloxypropoxy)-phenyl]-propaneand triethyleneglycol dimethacrylate (60/40 by weight) was prepared as the matrix phase in which 0.5 wt. % camphorquinone and 0.5 wt. % N-N'-dimethylaminoethyl methacrylate were dissolved as photoinitiator system. Glass fibers with three different diameters (14, 19, and 26 μm) were impregnated with the matrix resin using a soft brush. The FRCs were inserted into a 2 × 2 × 25 mm3 mold and cured using a light curing unit with an intensity of ca. 600 mW/cm2 . The FS of the FRCs was measured in a three-point bending method. The elastic modulus was determined from the slope of the initial linear part of stress-strain curve. The fracture surface of the composites was observed using scanning electron microscopy to study the fiber-matrix interface.

STATISTICAL ANALYSIS

The results were analyzed and compared using one-way ANOVA and Tukey's post-hoc test.

RESULTS

Although the FS increased as the diameter of fibers increased up to 19 μm (P < 0.05), no significant difference was observed between the composites containing fibers with diameters of 19 and 26 μm.

CONCLUSION

The diameter of the fibers influences the mechanical properties of the FRCs.

Dentin bond strength and degree of conversion evaluation of experimental self-etch adhesive systems

BACKGROUND

The aim of this study was to investigate the effect of different concentrations of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) monomer in one-step self-etch experimental adhesives on dentinal microshear bond strength (µSBS), their degree of conversion and bonded micro structure.

MATERIAL AND METHODS

Composite resin cylinders (Clearfil AP-X) were bonded on human sound molar dentinal surfaces by using five experimental one-step self-etching adhesives (1-SEAs) containing 0% (E0), 5% (E5), 10% (E10), 15% (E15), 20% (E20) (by weight) 10-MDP monomer and Clearfil S3 Bond (CS3) as a control. After 24 hours, microshear bond strength was tested. The degree of conversion was also measured using Fourier transform infrared spectroscopy. Interfacial ultrastructure was observed under a scanning electron microscope in all the groups.

RESULTS

A higher microshear bond strength was observed with adhesives containing 10% and 15% 10-MDP in comparison to study groups (P<.05). Clearfil S3 Bond and 10% MDP had a significantly greater degree of conversion than other groups (P<.05).

CONCLUSIONS

The amount of functional monomer in 1-SEAs influences both the bonding performance and degree of conversion; 10% 10-MDP showed the best combination of bond strength and degree of conversion. Key words:Self-etch adhesives, 10-MDP, bond strength, degree of conversion.

Assessments of antibacterial and physico-mechanical properties for dental materials with chemically anchored quaternary ammonium moieties: thiol-ene-methacrylate vs. conventional methacrylate system

OBJECTIVE

Fabrication of low shrinkage stress and strain dental resins containing highly available immobilized bactericidal moieties has been reported. The goal of this study is producing dental restorative materials with long-last antibacterial activity and reduced secondary caries. It is anticipated that antibacterial properties of quaternary ammonium moieties chemically immobilized in the backbone of dental resins is directly depended on accessibility of these functions. In the present study the antibacterial effect of a series of antibacterial monomers polymerized in a ternary thiol-ene-methacrylate system were compared with corresponding classical methacrylate system against Streptococcus mutans (an oral bacteria Strain). Physical and mechanical properties of dental materials obtained from these two systems were also evaluated and compared.

METHODS

The viscosities of the resin matrixes were measured on a MCR 300 rheometer. Degree of conversion (DC%) of monomers was measured using FTIR spectroscopy. The shrinkage-strain of photocured resins was measured using the bonded-disk technique. A universal testing machine combined with a stress measurement device was utilized to measure the polymerization-induced shrinkage stress. Viscoelastic properties of the samples were also determined by dynamic mechanical thermal analysis (DMTA). Assessment of antibacterial properties was performed through agar diffusion test (AD) to confirm non-release behavior of chemically anchored moieties. Quantitative assay of antibacterial activity was evaluated through direct contact test (DCT) against S. mutans. Direct contact cytotoxicity assay with fibroblast cell line L-929 was also performed to find more insight regarding cytotoxicity of the antibacterial matrixes. The data were analyzed and compared by ANOVA and Tukey HSD tests (significance level=0.05).

RESULTS

Neat methacrylate systems had significantly higher viscosity than thiol-ene-methacrylate analogous. The degree of conversion of methacrylate moieties in thiol-ene-methacrylate system was improved in comparison to conventional methacrylate system. Shrinkage stress and strain of thiol-ene-methacrylate system was lower than the neat methacrylate system. The thiol-ene-methacrylate systems show increased homogeneity and decreased glass transition temperature (Tg) and crosslink density (νc) in comparison to the neat methacrylate-based resins. The incorporated monofuctional quaternized monomer reduces degree of conversion, shrinkage stress and crosslink density of matrix. The results showed significant improvement in antibacterial activity and cytocompatibility of dental materials obtained from thiol-ene polymerization system.

SIGNIFICANCE

It was shown that with proper control of monomers molar ratio, significant improvement in antibacterial activity and cytocompatibility as well as acceptable mechanical properties can be attained for dental resins prepared through the application of thiol-ene polymerization methodology.

Temperature changes under demineralized dentin during polymerization of three resin-based restorative materials using QTH and LED units

Objectives

Light-curing of resin-based materials (RBMs) increases the pulp chamber temperature, with detrimental effects on the vital pulp. This in vitro study compared the temperature rise under demineralized human tooth dentin during light-curing and the degrees of conversion (DCs) of three different RBMs using quartz tungsten halogen (QTH) and light-emitting diode (LED) units (LCUs).

Materials and Methods

Demineralized and non-demineralized dentin disks were prepared from 120 extracted human mandibular molars. The temperature rise under the dentin disks (n = 12) during the light-curing of three RBMs, i.e. an Ormocer-based composite resin (Ceram. X, Dentsply DeTrey), a low-shrinkage silorane-based composite (Filtek P90, 3M ESPE), and a giomer (Beautifil II, Shofu GmbH), was measured with a K-type thermocouple wire. The DCs of the materials were investigated using Fourier transform infrared spectroscopy.

Results

The temperature rise under the demineralized dentin disks was higher than that under the non-demineralized dentin disks during the polymerization of all restorative materials (p < 0.05). Filtek P90 induced higher temperature rise during polymerization than Ceram.X and Beautifil II under demineralized dentin (p < 0.05). The temperature rise under demineralized dentin during Filtek P90 polymerization exceeded the threshold value (5.5℃), with no significant differences between the DCs of the test materials (p > 0.05).

Conclusions

Although there were no significant differences in the DCs, the temperature rise under demineralized dentin disks for the silorane-based composite was higher than that for dimethacrylate-based restorative materials, particularly with QTH LCU.

Comparison of various concentrations of tricalcium phosphate nanoparticles on mechanical properties and remineralization of fissure sealants

OBJECTIVE

The aim of this study was to investigate the mechanical properties (flexural strength, micro-shear bond strength) and remineralizing potential of fissure sealants by adding various concentrations of β-tricalcium phosphate nanoparticles.

MATERIALS AND METHODS

This in-vitro study consisted of five experimental groups containing prepared nano-fisssure sealants (1-5 wt.% β-TCP nanoparticles) and two control groups containing a prepared and a commercial fissure sealant. Flexural/micro-shear bond strength values were measured using Zwick test machine. Cavities on sixty healthy premolar teeth were filled with the fissure sealants containing 0-5 wt.% of nano β-TCP. The samples were assessed for remineralization under scanning electron microscopy (SEM) and EDAX. Kolmogorov-Smirnov test, One-way ANOVA and Tukey's Post Hoc analysis/HSD were used to analyze the data.

RESULTS

There was no significant difference between the flexural strengths/elastic modulus of the 0-5 wt.% nano β-TCP groups (p>0.05). The average flexural strength/elastic modulus of the prepared fissure sealant group (0%) was significantly higher than the commercial fissure sealant group (Clinpro) (p<0.05). There was no significant difference between micro-shear bond strengths of the experimental groups (1-5 wt.%), and between the commercial and the prepared (0%) fissure sealant groups (p>0.05). Examining the samples under SEM showed a significant increase in thickness of the intermediate layer with increasing concentrations of β-TCP nanoparticles (p<0.05).

CONCLUSION

Addition of 1-5 wt.% β-TCP nanoparticles to the fissure sealants significantly increased the remineralization potential without affecting the mechanical properties.

Effect of interface on mechanical properties and biodegradation of PCL HAp supramolecular nano-composites

This research explores the correlation between the structural properties of supramolecular biocomposites and their mechanical strength. Hybrid biocomposites composed of surface-modified hydroxyapatite nano-particles and supramolecular polycaprolactone (SP PCL), were prepared at different compositions, and their mechanical, thermal and viscoelastic properties as well as biodegradability, biocompatibility and cytotoxicity were evaluated in vitro. The results were compared with those for SP PCL/naked hydroxyapatite nano-composites. We show that surface modification of hydroxyapatite nanoparticles resulted in outstanding improvement of tensile strength and modulus up to 3.6 and 2.2-fold, respectively. At above 10 wt% HAp and 20 wt% HApUPy, heterogeneous nano-composites with inferior mechanical properties were obtained. Based on rheological (in steady shear mode) and small/wide angle X-ray scattering measurements, unusual improved mechanical properties were ascribed to the formation of supramolecular clusters around nanoparticles. In-vitro degradation of the supramolecular nano-composites was also studied to investigate the overall product biodegradation as well as toxicity of the degradation product(s).

Comparative evaluation of physical properties of four tissue conditioners relined to modeling plastic material

OBJECTIVE

Little is known about the interaction of tissue conditioners and modeling plastics. This study evaluates the influence of a variety of commercial tissue conditioners on alteration of viscoelastic properties of modeling plastics.

MATERIALS AND METHODS

In this in vitro study, the dynamic viscoelastic properties of four commercially available tissue conditioners (TC), Visco-gel (VG), GC Soft-Liner (SL), FITT (FT), and Coe Comfort (CC), relined to modeling plastics with a thickness of 2mm were evaluated after 1 and 7 days of water immersion with the use of storage modulus, loss modulus, and tan delta parameters. Values for these three parameters for each tissue conditioner were statistically analyzed by Kruskal Wallis and Mann Whitney tests with P value sets at<0.05.

RESULTS

Complex modulus and loss tangent values of TC were not significantly different among specimens containing 0, 2, 5 and 10 wt.%-SZ, respectively. In FT and TC containing 2 wt.%-SZ, these values were not significantly different between 1 and 28 days in both water- and saliva immersions.

CONCLUSION

The results suggest that relining with modeling plastics does affect TC's inherent dynamic viscoelastic properties, while the other tissue conditioners investigated may be found to have changed viscoelastic properties as a consequence of vicinity to the modeling plastics.

Gelation behavior of in situ forming gels based on HPMC and biphasic calcium phosphate nanoparticles

In this study, in situ forming gels are prepared using biphasic calcium phosphate (BCP) as filler and hydroxypropyl methylcellulose (HPMC) as a matrix exhibiting temperature-sensitive behavior. BCP was composed of β-tricalcium phosphate (β-TCP) with plate-like morphology and nano-sized hyadroxyapatite (HAp). Gel permeation chromatography (GPC) and rheological results showed that low molecular weight HPMC had lower gelation temperature. Effects of BCP content and HAp/β-TCP ratio on rheological behavior of the gels were investigated. According to the results, all samples showed a pseudoplastic behavior and their viscosity increased with increasing mineral phase, especially β-tricalcium phosphate. In order to investigate interaction mechanisms between the mineral phase and polymer and also the effects of ion release, particle size, hydrophobisity, and hydrophilisity, hydrophobic and hydrophilic silica with different particle sizes were also utilized. Results showed that factors affecting the hydrophobisity and hydrophilisity of solution may influence the rheological properties.